The germline is an immortal cell lineage essential for sexual reproduction. The germline cell cycle is likely to be very different from that of somatic cells in terms of developmental regulation, checkpoints, and cell division mechanisms. Our genetic studies in C. elegans have identified the emb-30 locus as a potential germline- specific cell cycle gene, required both for germ cells to proliferate, and for oocytes and spermatocytes to complete their meiotic divisions. Our analysis suggests that emb-30 oocytes are defective in exit from, but not entry into, meiotic metaphase: Following fertilization, they cannot progress to anaphase of meiosis I and arrest with a disorganized spindle. All subsequent embryonic events are blocked. In addition, emb-30 appears to play an essential role in germline proliferation and gamete formation. Importantly, all known emb-30 mutant phenotypes are specific to the germline and no defects in cell division or differentiation have been observed in any somatic cell. Based on antisense RNA phenocopy results, and genetic mapping results, emb-30 may encode a protein related to the SRPK1 protein kinase, which and phosphorylate splicing proteins and affect their nuclear compartmentalization. One model is that emb-30 plays a critical role in controlling the splicing of cell cycle regulators in the germline. Alternatively, emb-30 may directly affect the germline cell cycle, independent of splicing perhaps by affecting the meiotic spindle, or a spindle checkpoint. In order to define the role of emb-30 in germline development, we will test the following hypotheses: 1) that emb-30 is required specifically for meiosis and germline proliferation; 2) that emb-30 encodes a conserved protein kinase related to SRPK1; and 3) that emb-30 genetically interacts with gld-1 and glp-1, two genes that have been shown definitively to function in germline development. In order to test these hypotheses, we will: a) isolate and characterize new emb- 40 alleles; b) conduct an extensive molecular analysis of emb-30; c) analyze epistatic interactions with gld-1 and glp-1. The proposed studies will deepen our understanding of the meiotic cell cycle and may unify our view of mitosis and meiosis in the germline by identifying a shared essential component. Given the extensive biological similarities in the meiotic process between distantly related organisms, and evolutionary constraints on germline development, this research is likely to provide significant new insights into the control of meiosis in metazoans. The information gained from these studies will be useful for understanding human fertility/infertility for treating germline tumors.